1. Field of the Invention
The present invention relates to an image recording apparatus and method for recording image data as well as to a recording medium on which an image processing program for realizing the above image recording apparatus on a computer is recorded. The invention also relates to an image reproducing apparatus and method for reproducing a file generated by the above image recording apparatus as well as to a recording medium on which an image processing program for realizing the above image reproducing apparatus on a computer is recorded.
2. Description of the Related Art
In image recording apparatuses, usually, 8-bit-gradation (24 bits total in the case of 3-color data) image data are compressed and recorded in the form of a general-purpose compressed image file. Capable of being expanded by a general-purpose image-browsing program, such a general-purpose compressed image file has an advantage that it can be printed or displayed easily without using any dedicated software.
In recent years, there have been developed image recording apparatuses such as a digital still camera that can record raw data (i.e., data obtained by merely digitizing an output of an imaging device).
Raw data are image data that are faithful to an output of an imaging device and include fine gradation components (gradation signals). Therefore, raw data have an advantage that they are not easily impaired by complex data processing for designing, printing, and like purposes and their subtle gradation signals are not easily lost.
Incidentally, a general-purpose compressed image file of about 8-bit gradations as mentioned above has a relatively narrow gradation reproduction (tone reproduction) range and allows a high-luminance-side portion of an object to be reproduced with a gradation reproduction range of 140% white at most. Such a general-purpose compressed image file has a problem that high-luminance-side/low-luminance-side gradation components cannot be reproduced affluently with sufficient performance. It is desired that a general-purpose compressed image file have a gradation reproduction range of up to 200% white, and if possible, 400% white.
A general-purpose compressed image file is expressed with 8-bit gradations. This results in a problem that discontinuity of gradations becomes conspicuous when a file is subjected to image processing such as a contrast conversion.
On the other hand, raw data as mentioned above have a large number of quantization bits and hence allow fine middle range signals to be reproduced affluently with sufficient performance. However, raw data are given gradation characteristics and a data format that are specific to hardware such as a digital still camera. In standard form, general-purpose external apparatuses such as a printer and a monitor cannot deal with such raw data. That is, raw data are associated with a problem that it requires dedicated image processing and cannot be printed or displayed easily by a general-purpose external apparatus.
Image data such as raw data having a large number of quantization bits include fine middle range signals affluently. The degree of spatial redundancy of raw data is extremely lower than 8-bit-gradation image data. This results in a problem that conventional image compression methods that eliminate spatial redundancy cannot compress raw data into a file of a small size.